Silybum marianum (blessed thistle)

Silybum marianum

Photo courtesy Joseph DiTomaso

Silybum marianum (blessed thistle) is a winter annual or biennial with prickly leaves (family Asteraceae). It is widely spread throughout California in overgrazed pastures and along fencelines and other disturbed areas. Milk thistle produces tall, dense stands that outcompete native species.

Cal-IPC Inventory rating: Limited

Cal-IPC Resources on Silybum marianum

• California Invasive Plant Inventory Assessment Form (pdf) - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
• Cal-IPC News - Articles from our quarterly newsletter. Each issue is available as a pdf. List of articles on Silybum marianum.
• Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium. List of articles on Silybum marianum.
• California distribution map - Maps based on survey data from county Weed Management Areas. These maps are the product of those working in the field and are not intended to be definitive.

Cal-IPC News Articles

• Massera, J. (2001). More about Italian thistle. CalEPPC News. 9: 14.
• Perala, C., D. A. Hoover, et al. (1993). Control of exotic plants in an herbaceous understory. CalEPPC News. 1: 4-6.

Cal-IPC Symposium Proceedings

• Archbald, G. (1998). Mechanical control methods: beyond weed bashing. California Exotic Pest Plant Council Symposium '98. Ontario, CA.
• Lair, K., N. Ritter, et al. (2006). Restoration of retired San Joaquin Valley farmlands using herbicides and activated charcoal. Cal-IPC Symposium. Rohnert Park, CA.
• Pitcairn, M. J. and D. M. Woods (1998). Control methods: biological control. California Exotic Pest Plant Council Symposium 1998. Ontario, CA.

Other Resources on Silybum marianum

• USDA PLANTS database - Federal database with information on identification and distribution, and links to websites in individual states.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from the UC Berkeley Jepson Herbarium.
• CalFlora - Distribution information by county based on submitted observations and herbarium specimens.
• The Nature Conservancy Management Summary - Information compiled by TNC land managers. Photos included for some species.
• CalPhotos - Images of plants taken mostly in California.

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